From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yafang Shao Subject: [PATCH net-next] tcp: forbid direct reclaim if MSG_DONTWAIT is set in send path Date: Tue, 9 Oct 2018 20:05:18 +0800 Message-ID: <1539086718-4119-2-git-send-email-laoar.shao@gmail.com> References: <1539086718-4119-1-git-send-email-laoar.shao@gmail.com> Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Yafang Shao To: edumazet@google.com, davem@davemloft.net Return-path: In-Reply-To: <1539086718-4119-1-git-send-email-laoar.shao@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org By default, the sk->sk_allocation is GFP_KERNEL, that means if there's no enough memory it will do both direct reclaim and background reclaim. If the size of system memory is great, the direct reclaim may cause great latency spike. When we set MSG_DONTWAIT in send syscalls, we really don't want it to be blocked, so we'd better clear __GFP_DIRECT_RECLAIM when allocate skb in the send path. Then, it will return immediately if there's no enough memory to be allocated, and then the appliation has a chance to do some other stuffs instead of being blocked here. Signed-off-by: Yafang Shao --- net/ipv4/tcp.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 43ef83b..fe4f5ce 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -1182,6 +1182,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size) bool process_backlog = false; bool zc = false; long timeo; + gfp_t gfp; flags = msg->msg_flags; @@ -1255,6 +1256,9 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size) /* Ok commence sending. */ copied = 0; + gfp = flags & MSG_DONTWAIT ? sk->sk_allocation & ~__GFP_DIRECT_RECLAIM : + sk->sk_allocation; + restart: mss_now = tcp_send_mss(sk, &size_goal, flags); @@ -1283,8 +1287,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size) } first_skb = tcp_rtx_and_write_queues_empty(sk); linear = select_size(first_skb, zc); - skb = sk_stream_alloc_skb(sk, linear, sk->sk_allocation, - first_skb); + skb = sk_stream_alloc_skb(sk, linear, gfp, first_skb); if (!skb) goto wait_for_memory; -- 1.8.3.1